## What's the influence of the integration time on the quality of the acoustic map of a vehicle passing by?

The quality of a resulting acoustic map of the NoiseImage PassBy 2D module depends primarily on the integration time. It determines the length of the signal which is used for analysing each of the $$n$$=1...,N possible source points. Similarly, integration time can be interpreted as the length of the trajectory (scan width) on which one possible sound source $$n$$ is tracked by the microphone array. A general prediction of a suitable integration time cannot be provided since it depends directly on the velocity $$v$$ of the measured object.

As an application example, the results of a high speed train with an average velocity of
$$v$$=78.6 m/s and different integration times are shown for the third octave band at 3.15 kHz and dynamics of 6.5 dBA. A short integration time of 7 ms (corresponds to scan width of 0.55 m, see Figure 1) may lead to a source representation which divides large connected sound sources such as the wheel set into a group of single sources. Furthermore, the number of analysed samples becomes too small to represent even a single period at low frequencies. However, long integration times such as 63 ms (corresponds to scan with of  4.95 m, see Figure 2) lead to a decrease of the acoustic maps dynamics and to a blurry source representation. Additionally, calculation time increases with a long integration time. A solution with reasonable source representation and calculation time can be found at an integration time of 25 ms (corresponds to scan width of 1.96 m, see Figure 3).